A significant cause of chronic injury to vascular tissues in humans may be one or more of the common viral infections which involve viremia, hence viral exposure and infection of the vascular tissues themselves. Likewise, bacteremia may cause chronic infection of vascular tissues. Such injury in the large vessels could initiate or potentiate the development of fatty deposits and, eventually, atherosclerosis. We will seek experimental evidence for this in several way . Cell cultures will be prepared from human vascular tissues obtained at autopsy; these cultures will be incubated for long periods of time and treated in various ways to enhance the emergence of latent or masked viruses. Viral detection techniques to be used include immunofluorescence microscopy, radioimmunoassay, electron microscopy, hemadsorption and observation for cytopathic effects. The presence of viral antigens will be sought, whether associated with infectious virus or not. We will attempt to detect viral and bacterial antigens or antigen-antibody complexes directly in vascular tissues (especially tissues where there is obvious injury or disease). The spectrum of viruses which will adsorb to and replicate in human vascular tissues will be studied in both cell and organ cultures of arteries from several individuals. Experimental models will be used to determine whether antigen-antibody complexes will deposit in blood vessels and, if so, what are the mechanisms and consequences of such deposits.